Microporous membranes find advantageous application in the filtration field. Such membranes can be produced with particles that produce chains of defects in the membrane, which defects correspond to the path of the particles. These defects make the areas around them sensitive to certain chemical agents. Exposure of the membrane to such chemical agents makes it possible to produce pores along the path of the particles, and thus the filtration characteristics of the microporous membrane.
It has been known to produce porous membranes from materials, such as polyethylene terephthalate (PET), polypropylene (PP) and polycarbonates. The paths or defects in the polymers are typically formed by irradiating the polymers with heavy ions, such as krypton (Kr), xenon (Xe), argon (Ar) and uranium (U). Irradiating polymers with such heavy ions requires relatively high energy level particle accelerators, such as high-energy cyclotrons. Following irradiation, the polymers are etched to form the pores.
One problem associated with the conventional methods of producing pore membranes is that the thickness of the materials used is limited due to the limited depth of penetration of the aforementioned heavy ions. For example, the maximum thickness of the foregoing materials that could be used when irradiated with xenon, argon and krypton is approximately 10 microns.
Another problem with the conventional methods of producing pore membranes is that they do not lend themselves to forming pore membranes from fluoropolymers, such as polytetrafluoroethylene (PTFE). In this respect, chemical and physical problems exist with trying to form nuclear pores in fluoropolymers, such as polytetrafluoroethylene (PTFE).
A third problem associated with the conventional methods of producing pore membranes is the cost of such processes. Cyclotrons, typically required to produce heavy ions with the requisite high kinetic energy to produce nuclear pores, are extremely expensive.
The present invention overcomes these and other problems, and provides a method of forming microporous membranes from fluoropolymers, such as polytetrafluoroethylene (PTFE).